Autoantibodies to IA2 (IA2A), a member of the protein tyrosine phosphatase family, are found in 50-75% of type 1 diabetic patients at and prior to disease onset. They are generally more prevalent in younger onset patients and are associated with rapid progression to disease. Measurement of autoantibodies to IA2 has been shown to be of significant value for the diagnosis and prediction of type 1 diabetes in first-degree relatives of diabetic patients.